1. Field of the Invention
The present invention relates generally to an actively controlled automotive suspension system for suppressing attitude change of a vehicular body and absorbing road shock for achieving both of riding comfort and driving stability. More specifically, the invention relates to an improvement in and relating to layout of components of the actively controlled suspension system for better performance.
2. Description of the Prior Art
Actively controlled suspension systems have been proposed as advanced technology for automotive suspension systems which can achieve both of riding comfort and driving stability. For example, U.S. Pat. No. 4,702,490, issued Oct. 27, 1987 discloses one of typical construction of the actively controlled hydraulic suspension system which includes a hydraulic cylinder defining a working chamber associated with a hydraulic pressure source. A pressure control valve is disposed within a hydraulic circuit connecting the hydraulic pressure source for adjusting the pressure in the working chamber for controlling suspension characteristics so that it may be adapted to a vehicle driving condition. The pressure control valve is electrically controlled valve position for introducing and draining the pressurized working fluid in the working chamber, by a control unit. The control unit receives a plurality of suspension control parameters, such as bounding and rebounding stroke between the vehicle body and a suspension member rotatably supporting a road wheel, longitudinal and/or lateral acceleration exerted on the vehicle body. The control unit performs anti-pitching, anti-rolling, suppression of bouncing and so forth.
In such the prior proposed actively controlled suspension system, the pressure control valve is constructed to include a valve spool for selectively establishing and blocking fluid communication between the working chamber of the hydraulic cylinder and the hydraulic pressure source. The valve spool is disposed within a valve bore for thrusting movement as activated by an electrically driven actuator, such as an electromagnetic solenoid. For such valve spool, acceleration exerted on the vehicle body tends to influence to unintentionally causing shifting the position for causing variation of the fluid pressure in the working chamber. This degrades precision level of suspension control.
For example, when the pressure control valve is arranged in a position to place the valve bore laterally and perpendicular to the longitudinal axis of the vehicle body. The valve spool is then movable in lateral direction with respect to the vehicle body. In such case, the valve spool can be subject lateral force during cornering. Assuming that the vehicle is running through the left-hand curve, and that the vehicle body is subject right-ward lateral force to cause right-hand rolling, the fluid pressure in the working fluid of the pressure control valves for right side suspension systems, i.e. right-front and right-rear suspension systems, are increased for suppressing lowering right side of the vehicle body. On the other hand, the fluid pressure in the working chamber in the hydraulic cylinder is decreased for avoiding excessive expansion of the working chamber for suppressing lifting up of the left side of the vehicle body. During such activity of the actively controlled suspension system, the right-ward force is exerted on respective valve spools of the pressure control valves to cause shifting. If this causes the pressure control valves for the right side suspension system to shift in a direction for decreasing the fluid pressure and the pressure control valves for the left side suspension system to shift in a direction for increasing the fluid pressure, vehicle body rolling is amplified.
In order to avoid influence of the external force for the pressure control valve, it may be necessary to restrict movement of the valve spool by means of a spring which has sufficient spring force. In such case, the spring force may be selected so as not to be overcome by the external force. This, on the other hand, serves as resistance against control force for positioning the valve spool for performing active suspension control. Since the valve position in the pressure control valve must have sufficiently high response characteristics so that the damping characteristics of the hydraulic cylinder can be timely adjusted. This requires big capacity of the actuator and big electric power to drive the actuator for causing quick shift of the valve spool. The bigger capacity of actuator and bigger spring force of the springs are necessarily bulky to prevent the pressure control valve to be satisfactorily compact to conveniently place on the vehicle body without causing interference with various vehicular components.